Reducing cyclic variation of a gasoline rotary engine by hydrogen addition under various operating conditions

In the present paper, the cyclic variations of a hydrogen-blended gasoline rotary engine operated under various conditions were experimentally investigated. The experiments were carried out on a modified hydrogen-gasoline dual-fuel rotary engine equipped with an electronically-controlled fuel injection system. An electronic control module was specially made to command the fuel injection, excess air ratio and hydrogen volumetric fraction. The tested engine was first run at idle condition with a speed of 2400 rpm and then operated at 4500 rpm to investigate the cyclic variations of a hydrogen-enriched gasoline rotary engine under different hydrogen volumetric percentages in the total intake, excess air ratios and spark timings. The experimental results demonstrated that the coefficient of variations (in peak pressure, engine speed, flame development period and flame propagation period) of the gasoline rotary engine were distinctly decreased with the increase of hydrogen volume fraction under all the tested conditions. In particular, at idle and stoichiometric conditions, the coefficient of variation in CA0-10 and CA10-90 were reduced from 9.25% to 5.01%, 15.40% to 8.70%, respectively.     

Idle performance of a hydrogen/gasoline rotary engine at lean condition

Because of the limit of properties of gasoline and irregular design of chamber, the pure gasoline rotary engine generally encounters partial burning, increased noxious emissions or even misfire at lean conditions. This situation could be deteriorated at idle because of the high variation in the intake charge and low combustion temperature. Hydrogen addition is proved to remit the deterioration of performance of sparked-ignited (SI) engines at idle and lean conditions. This paper conducted an experiment on a modified rotary engine equipped with gasoline and hydrogen port-injection systems to explore the performance of a hydrogen–gasoline rotary engine (HGRE) at idle and lean conditions. An electronic management unit (EMU) was invented to manage spark and fuel injection. Excess air ratio (λ) and hydrogen volumetric fraction in the total intake (${\alpha }_{{\text{H}}_2}$) were also governed through the EMU. For this study, the HGRE was operating at idle and ${\alpha }_{{\text{H}}_2}$ was kept at 0% and 3%, respectively. For a specific ${\alpha }_{{\text{H}}_2}$, gasoline flow rate was reduced to make the HGRE run at desired λ. Results indicated that engine fluctuation and fuel energy flow rate were both decreased after hydrogen addition. Combustion duration was cut down and central heat release point was advanced after hydrogen addition. Peak chamber temperature (T_max), pressure and heat release were enhanced after hydrogen blending. HC, CO and CO₂ emissions were simultaneously reduced because of hydrogen enrichment. Specifically, at λ = 1.00, HC, CO and CO₂ emissions were respectively reduced from 42,411 to 26,316 ppm, 1.86 to 0.78% and 9.96 to 8.58% when 3% hydrogen was added.     

Reducing the idle speed of a gasoline rotary engine with hydrogen addition

This paper presented an experimental study about the idle performance of a rotary engine fueled with hydrogen and gasoline blends. The idle speed was reduced from original 2400 to 2300 and 2200 rpm, and hydrogen energy percentage (β_H2) was varied from 0% to 35.0%. Test results showed that cyclic variation was raised with the decrease of idle speed whereas reduced with the increase of β_H2. Both decreasing idle speed and increasing β_H2 were effective on reducing engine fuel consumption. Total fuel energy flow rate was effectively dropped from 22.4 MJ/h under “2400 rpm and β_H2 = 0%” to 20.01 MJ/h under “2200 rpm and β_H2 = 35.0%”. Combustion duration was reduced through increasing β_H2. HC and CO emissions were dropped with the increase of β_H2, but increased after reducing idle speed. CO₂ emission was decreased after reducing idle speed and adding hydrogen.     

A comparative study on performance of the rotary engine fueled hydrogen/gasoline and hydrogen/n-butanol

The comparative study on performance of the hydrogen/gasoline and hydrogen/n-butanol rotary engines was conducted in the present paper. Considering the stable operation of the engine, for both hydrogen/gasoline case and hydrogen/n-butanol case, the operating conditions were set at: 4000 rpm (engine speed), 35 kPa (intake pressure) and 30 °CA BTDC (spark timing). The total excess air ratio of mixture was maintained at 1.0 through all the tests. The testing results displayed that hydrogen enrichment improved performance of both gasoline and n-butanol rotary engines. To be more specific, brake thermal efficiency was increased, flame development and propagation periods were shortened, the coefficient of variation in flame propagation period was decreased, and the emissions of HC and CO were decreased. NOx emissions were mildly increased after hydrogen addition. Besides, hydrogen/n-butanol rotary engine possessed the similar performance to hydrogen/gasoline rotary engine.     

Effect of hydrogen addition on combustion and emissions performance of a spark ignition gasoline engine at lean conditions

Hydrogen has many excellent combustion properties that can be used for improving combustion and emissions performance of gasoline-fueled spark ignition (SI) engines. In this paper, an experimental study was carried out on a four-cylinder 1.6 L engine to explore the effect of hydrogen addition on enhancing the engine lean operating performance. The engine was modified to realize hydrogen port injection by installing four hydrogen injectors in the intake manifolds. The injection timings and durations of hydrogen and gasoline were governed by a self-developed electronic control unit (DECU) according to the commands from a calibration computer. The engine was run at 1400 rpm, a manifold absolute pressure (MAP) of 61.5 kPa and various excess air ratios. Two hydrogen volume fractions in the total intake of 3% and 6% were applied to check the effect of hydrogen addition fraction on engine combustion. The test results showed that brake thermal efficiency was improved and kept roughly constant in a wide range of excess air ratio after hydrogen addition, the maximum brake thermal efficiency was increased from 26.37% of the original engine to 31.56% of the engine with a 6% hydrogen blending level. However, brake mean effective pressure (Bmep) was decreased by hydrogen addition at stoichiometric conditions, but when the engine was further leaned out Bmep increased with the increase of hydrogen addition fraction. The flame development and propagation durations, cyclic variation, HC and CO₂ emissions were reduced with hydrogen addition. When excess air ratio was approaching stoichiometric conditions, CO emission tended to increase with the addition of hydrogen. However, when the engine was gradually leaned out, CO emission from the hydrogen-enriched engine was lower than the original one. NO_x emissions increased with the increase of hydrogen addition due to the raised cylinder temperature.     

Analysis of the particulate emissions and combustion performance of a direct injection spark ignition engine using hydrogen and gasoline mixtures

Three different fractions (2%, 5%, and 10% of stoichiometric, or 2.38%, 5.92%, and 11.73% by energy fraction) of hydrogen were aspirated into a gasoline direct injection engine under two different load conditions. The base fuel was 65% iso-octane, and 35% toluene by volume fraction. Ignition sweeps were conducted for each operation point. The pressure traces were recorded for further analysis, and the particulate emission size distributions were measured using a Cambustion DMS500. The results indicated a more stable and faster combustion as more hydrogen was blended. Meanwhile, a substantial reduction in particulate emissions was found at the low load condition (more than 95% reduction either in terms of number concentration or mass concentration when blending 10% hydrogen). Some variation in the results occurred at the high load condition, but the particulate emissions were reduced in most cases, especially for nucleation mode particulate matter. Retarding the ignition timing generally reduced the particulate emissions. An engine model was constructed using the Ricardo WAVE package to assist in understanding the data. The simulation reported a higher residual gas fraction at low load, which explained the higher level of cycle-by-cycle variation at the low load.     

Effect of hydrogen nanobubble addition on combustion characteristics of gasoline engine

Hydrogen is an attractive energy source for improving gasoline engine performance. In this paper, a new hydrogen nanobubble gasoline blend is introduced, and the influence of hydrogen nanobubble on the combustion characteristics of a gasoline engine is experimentally investigated. The test was performed at a constant engine speed of 2000 rpm, and engine load of 40, 60, and 80%. The air-to-fuel equivalence ratio (λ) was adjusted to the stoichiometric (λ = 1), for both gasoline, and the hydrogen nanobubble gasoline blend. The results show that the mean diameter and concentration of hydrogen nanobubble in the gasoline blend are 149 nm and about 11.35 × 10⁸ particles/ml, respectively. The engine test results show that the power of a gasoline engine with hydrogen nanobubble gasoline blend was improved to 4.0% (27.00 kW), in comparison with conventional gasoline (25.96 kW), at the engine load of 40%. Also, the brake specific fuel consumption (BSFC) was improved, from 291.10 g/kWh for the conventional gasoline, to 269.48 g/kWh for the hydrogen nanobubble gasoline blend, at the engine load of 40%.     

An experimental investigation of hydrogen-enriched gasoline in a Wankel rotary engine

The Wankel rotary engine is a potential alternative to the reciprocating engine in hybrid applications because of its favorable energy to weight ratio. In this study, a Wankel rotary engine was modified to run on a hydrogen–gasoline blend. Hydrogen enrichment improved the performance of a lean-burn spark-ignition rotary engine operating at high speed and wide open throttle conditions with the original ignition timing, using 0%, %2, 4%, 5%, 7%, and 10% hydrogen energy fractions at the intake. The experimental results showed that adding hydrogen to gasoline in the engine improved the thermal efficiency and the power output. Hydrocarbon and carbon monoxide emissions were reduced while nitrogen oxide emissions increased with the increase of hydrogen fraction.     

Improving burning speed by using hydrogen enrichment and turbulent jet ignition system in a rotary engine

Low flame speed restrains engine efficiency and increases HC emissions in rotary engines. Hydrogen addition and turbulent jet ignition have a great potential in increasing engine performance as they increase fuel burning speed. In this study, the classical R13b-Renesis Wankel engine and a modified one with a turbulent jet ignition configuration are numerically investigated by using hydrogen as a supplement. Eccentric motion of the rotor was generated by using User Defined Function in ANSYS-Fluent software. Pure methane and methane blended with 3% and 6% hydrogen energy fractions were used as fuels in the calculations. Combustion was modeled by using reduced mechanism of hydrogen-methane combustion having 22 species and 104 reactions. The Wankel engine was simulated at 2000 rpm speed and partial load conditions. At first, classical engine configuration having two spark plugs was simulated with pure methane. Then, hydrogen blended methane simulations were conducted to investigate the benefits of the hydrogen addition. Similar procedure was applied for the turbulent jet ignition application. The results show that both approaches are effective on increasing the burning speed of the fuel. It is revealed that hydrogen addition increases the indicated mean effective pressure (IMEP) by 1.8% and 5.2% for 3% and 6% hydrogen fraction cases respectively in the classical engine. Turbulent jet ignition with pure methane increases IMEP by 4.7% compared to the classical engine. Hydrogen addition only in pre-chamber is effective as much as 6% hydrogen fraction of classical engine. As the burning speed is increased by the application of these methods, CO and HC emissions are reduced and NO emission is increased. It is concluded that benefits of hydrogen addition and turbulent jet ignition applications can be optimized for both reducing harmful emissions and increasing engine performance.     

Numerical simulation of hydrogen combustion process in rotary engine with laser ignition system

In this paper the combustion and ignition process in the hydrogen-fueled peripheral-ported rotary engine with single and dual laser ignition systems was studied numerically. The computational method was established for the process simulation including interaction between turbulence and chemical reactions. The detailed chemical kinetic model of hydrogen combustion was used. It was shown that the ignition and combustion process in the H₂-fueled rotary engine is highly transient with specific distortion and stretching of the combustion front in the combustion chamber due to complex motion of the rotor relative to the engine housing. The single and dual laser ignition systems were simulated to compare the ignition efficiency and the rate of hydrogen burning out. The evaluation of pressure in the combustion chamber was performed and compared with the experimental data obtained for the rotary engine fueled by natural gas. It was shown that the H₂-fueled rotary engine with the dual laser ignition system has potential application in alternative automotive industry due to high efficiency and near-zero carbon-based emission.     

Investigation on combustion and emissions characteristics of a hydrogen-blended n-butanol rotary engine

In this paper, a rotary engine equipped with an n-butanol and hydrogen port-injection system was developed to investigate the combustion and emissions characteristics of a hydrogen-blended n-butanol rotary engine at part load and stoichiometric conditions. A self-developed hybrid electronic control unit was adopted to adjust the injection durations of n-butanol and hydrogen. The rotary engine was run under the conditions of 4000 rpm, a manifold absolute pressure of 35 kPa and a fixed spark timing of 45 °CA before the top dead center during the whole testing operation. The hydrogen volumetric fraction in the total intake was varied from 0% to 6.30%. The test results manifested that the brake thermal efficiency and chamber temperature were simultaneously increased with hydrogen addition. The hydrogen supplement obviously shortened flame development and propagation periods. Both chamber pressure integral heat release fraction versus crank angle were increased when the hydrogen fraction was enhanced. HC emissions were reduced by 54.5% when hydrogen volume fraction was raised from 0% to 6.30%, CO and CO₂ emissions were also reduced after increasing hydrogen blending fraction. NOx emissions were mildly elevated due to the improved chamber temperature.     

Comparisons of hydrogen and gasoline combustion knock in a spark ignition engine

Combustion knock is one of the primary constraints limiting the performance of spark-ignition hydrogen fuelled internal combustion engines (H2-ICE) as it limits the torque output and efficiency, particularly as the equivalence ratio nears stoichiometric operation. Understanding the characteristic of combustion knock in a H2-ICE will provide better techniques for its detection, prevention and control while enabling operation at conditions of improved efficiency.

Engine studies examining combustion knock characteristics were conducted with hydrogen and gasoline fuels in a port-injected, spark-ignited, single cylinder cooperative fuel research (CFR) engine. Characterization of the signals at varying levels of combustion knock from cylinder pressure and a block mounted piezoelectric accelerometer were conducted including frequency, signal intensity, and statistical attributes. Further, through the comparisons with gasoline combustion knock, it was found that knock detection techniques used for gasoline engines, can be applied to a H2-ICE with appropriate modifications. This work provides insight for further development in real time knock detection. This would help in improving reliability of hydrogen engines while allowing the engine to be operated closer to combustion knock limits to increase engine performance and reducing possibility of engine damage due to knock.     

Idle performance of a hydrogen rotary engine at different excess air ratios

Rotary engine has flat chamber and longs for fuel with high flame speed and small quenching distance. Hydrogen has many excellent characteristics that are suitable for the rotary engine. In this paper, the performance of a rotary engine fueled with pure hydrogen at different excess air ratios was experimentally investigated. The investigation was carried out on a single-rotor hydrogen-fueled rotary engine equipped with port fuel injection system. An online electronic control module was used to govern the hydrogen injection duration and excess air ratio. In this study, the engine was operating at the idle speed of 3000 rpm and different excess air ratios varied from 0.993 to 1.283. The test results demonstrated that the fuel energy flow rate of the hydrogen rotary engine and engine stability were reduced with the increase of excess air ratio. When the excess air ratio increased from 0.993 to 1.283, the hydrogen energy flow rate was decreased from 14.91 to 11.55 MJ/h. Both the flame development and propagation periods were increased with excess air ratio. CO emission was negligible, but HC, CO₂ and NOx emissions were still detected due to the evaporation and possible burning of the lubrication-used gasoline, and oxidation reaction of nitrogen of the intake air.     

Improving the performance of a gasoline engine with the addition of hydrogen-oxygen mixtures

The limited fossil fuel reserves and severe environmental pollution have pushed studies on improving the engine performance. This paper investigated the effect of hydrogen-oxygen blends (hydroxygen) addition on the performance of a spark-ignited (SI) gasoline engine. The test was performed on a modified SI engine equipped with a hydrogen and oxygen injection system. A hybrid electronic control unit was adopted to govern the opening and closing of hydrogen, oxygen and gasoline injectors. The standard hydroxygen with a fixed hydrogen-to-oxygen mole fraction of 2:1 was applied in the experiments. Three standard hydroxygen volume fractions in the total intake gas of 0%, 2% and 4% were adopted. For a given hydroxygen blending level, the gasoline injection duration was adjusted to enable the excess air ratio of the fuel-air mixtures to increase from 1.00 to the engine lean burn limit. Besides, to compare the effects of hydroxygen and hydrogen additions on the performance of a gasoline engine, a hydrogen-enriched gasoline engine was also run at the same testing conditions. The test results showed that the hydroxygen-blended gasoline engine produced higher thermal efficiency and brake mean effective pressure than both of the original and hydrogen-blended gasoline engines at lean conditions. The engine cyclic variation was eased and the engine lean burn limit was extended after the standard hydroxygen addition. The standard hydroxygen enrichment contributed to the decreased HC and CO emissions. CO from the standard hydroxygen-enriched gasoline engine is also lower than that from the hydrogen-enriched gasoline engine. But NOx emissions were increased after the hydroxygen addition.     

Effect of hydrogen addition on the idle performance of a spark ignited gasoline engine at stoichiometric condition

With regard to the improvement of efficiency, combustion stability, and emissions in a gasoline engine at idle condition, an experimental study aimed at improving engine idle performance through hydrogen addition was carried out on a 4-cylinder gasoline-fueled spark ignited (SI) engine. The engine was modified to be fueled with the mixture of gasoline and hydrogen injected into the intake ports simultaneously. A self-developed electronic control unit (DECU) was dedicatedly used to control the injection timings and injection durations of gasoline and hydrogen. Other parameters, such as spark timing and idle valve opening, were controlled by the original engine electronic control unit (OECU). Various hydrogen enrichment levels were selected to investigate the effect of hydrogen addition on engine speed fluctuation, thermal efficiency, combustion characteristics, cyclic variation and emissions under idle and stoichiometric conditions. The experimental results showed that thermal efficiency, combustion performance, NO_x emissions are improved with the increase of hydrogen addition level. The HC and CO emissions first decrease with the increasing hydrogen enrichment level, but when hydrogen energy fraction exceeds 14.44%, it begins to increase again at idle and stoichiometric conditions.     

An experimental study on ignition timing of hydrogen Wankel rotary engine

The hydrogen-fueled Wanke rotary engine is a promising power system that has both high power and eco-friendly properties. This work investigated the effect of ignition timing on a dual-spark plugs synchronous-ignition hydrogen-fueled Wankel rotary engine under low speed, part load and lean combustion. The results show that with delaying the ignition timing, CA0-10 is shortened first and then lengthened and CA10-90 is consistently shortened. When the CA50 is located between 35 and 40°CA ATDC, the maximum brake torque can be realized. Besides, the selection of ignition timing needs to consider the “trade-off” relationship between the combustion phase and corresponding in-cylinder pressure. The maximum brake torque ignition timing is between 5 and 10°CA ATDC. And there is also a “trade-off” relationship between stability and thermal load when ignition timing is selected. In addition, HC and NO emissions will not become the problem limiting the power performance of hydrogen-fueled Wankel rotary engine under this operating condition.     

Effect of addition of hydrogen and TiO2 in gasoline engine in various exhaust gas recirculation ratio

The effects of hydrogen ratios on combustion and emission characteristics of gasoline engine were studied under different exhaust gas recirculation (EGR), ignition timing and ignition pressure. The test performed in a modified gasoline direct ignition engine at different hydrogen ratios of 0%, 5%, 10% and 25%. In addition, the EGR rate set to 0%, 5%, 10% and 20% to study the combustion and emission characteristics. Addition to the different hydrogen fractions, 5% of TiO₂ is added to increase the combustion characteristics with reduced emission. Regarding the results of the current study, the engine torque increases by 15% due to the addition of hydrogen in gasoline, while mechanical efficiency is improved by achieving a large throttle opening. At the same time, NOx emission decreased by 62% compared to the unmodified engine due to the influence of EGR, hydrogen ratio and high oxygen concentration TiO₂. Moreover, the emission of CO and HC also reduced due to the influence of hydrogen fuel. Additionally, few more tests are taken to monitor the effect of the injection pressure for the hydrogen fuel. Higher injection reports higher effective thermal efficiency at 4 MPa and lower NOx. Reasonable injection pressure results in shorten flame development period.     

Enhancing idle performance of an n-butanol rotary engine by hydrogen enrichment

Rotary engine generally sustains poor fuel economy and emissions performance at idle condition. Hydrogen has excellent physicochemical properties that can serve as an enhancer to improve the performance of the original engine. In this paper, a modified rotary engine equipped with dual fuel (hydrogen and n-butanol) port injection system and electronic ignition module was developed to explore the influence of hydrogen supplement on enhancing the idle performance of n-butanol rotary engine. In this study, the engine was run at the idle and stoichiometric with the original spark timing. Hydrogen volume percentage in the total intake was gradually increased from 0% to 7.9% by adjusting the fuel flow rate of n-butanol. The experimental results indicated that the engine instability and fuel energy flow rate were both reduced by enlarging the hydrogen supplying level. Combustion periods were shortened thanks to the enrichment of hydrogen. The peak chamber temperature was heightened as hydrogen fraction increased due to the improved combustion. HC and CO emissions were severally reduced by 50.4% and 85.8% when the hydrogen volume percentage was raised from 0% to 7.9%. However, NOx emissions were mildly increased because of the raised chamber temperature by increasing hydrogen fraction.     

Effects of hydrogen addition and cylinder cutoff on combustion and emissions performance of a spark-ignited gasoline engine under a low operating condition

Because of the low combustion temperature and high throttling loss, SI (spark-ignited) engines always encounter dropped performance at low load conditions. This paper experimentally investigated the co-effect of cylinder cutoff and hydrogen addition on improving the performance of a gasoline-fueled SI engine. The experiment was conducted on a modified four-cylinder SI engine equipped with an electronically controlled hydrogen injection system and a hybrid electronic control unit. The engine was run at 1400 rpm, 34.5 Nm and two cylinder cutoff modes in which one cylinder and two cylinders were closed, respectively. For each cylinder closing strategy, the hydrogen energy fraction in the total fuel (βH₂)$\left({\beta }_{{\text{H}}_2}\right)$ was increased from 0% to approximately 20%. The test results demonstrated that engine indicated thermal efficiency was effectively improved after cylinder cutoff and hydrogen addition, which rose from 34.6% of the original engine to 40.34% of the engine operating at two-cylinder cutoff mode and βH₂=20.41%${\beta }_{{\text{H}}_2}=20.41\%$. Flame development and propagation periods were shortened with the increase of the number of closed cylinders and hydrogen blending ratio. The total cooling loss for all working cylinders, and tailpipe HC (hydrocarbons), CO (carbon monoxide) and CO₂ (carbon dioxide) emissions were reduced whereas tailpipe NO_x (nitrogen oxide) emissions were increased after hydrogen addition and cylinder closing.     

Effect of hydrogen addition on combustion and emissions performance of a spark-ignited ethanol engine at idle and stoichiometric conditions

Regarding the limited fossil fuel reserves, the renewable ethanol has been considered as one of the substitutional fuels for spark ignition (SI) engines. But due to its high latent heat, ethanol is usually hard to be well evaporated to form the homogeneous fuel–air mixture at low temperatures, e.g., at idle condition. Compared with ethanol, hydrogen possesses many unique combustion and physicochemical properties that help improve combustion process. In this paper, the performance of a hydrogen-enriched SI ethanol engine under idle and stoichiometric conditions was investigated. The experiment was performed on a modified 1.6 L SI engine equipped with a hydrogen port-injection system. The ethanol was injected into the intake ports using the original engine gasoline injection system. A self-developed hybrid electronic control unit (HECU) was adopted to govern the opening and closing of hydrogen and ethanol injectors. The spark timing and idle bypass valve opening were governed by the engine original electronic control unit (OECU), so that the engine could operate under its original target idle speed for each testing point. The engine was first fueled with the pure ethanol and then hydrogen volume fraction in the total intake gas was gradually increased through increasing hydrogen injection duration. For a specified hydrogen addition level, ethanol flow rate was reduced to keep the hydrogen–ethanol–air mixture at stoichiometric condition. The test results showed that hydrogen addition was effective on reducing cyclic variations and improving indicated thermal efficiency of an ethanol engine at idle. The fuel energy flow rate was reduced by 20% when hydrogen volume fraction in the intake rose from 0% to 6.38%. Both flame development and propagation periods were shortened with the increase of hydrogen blending ratio. The heat transfer to the coolant was decreased and the degree of constant volume combustion was enhanced after hydrogen addition. HC and CO emissions were first reduced and then increased with the increase of hydrogen blending fraction. The acetaldehyde emission from the hydrogen-enriched ethanol engine is lower than that from the pure ethanol engine. However, the addition of hydrogen tended to increase NO_x emissions from the ethanol engine at idle and stoichiometric conditions.